Multilayer sheet and container

Abstract

A multilayer sheet comprising: a first laminate having, in order, a surface layer, a first adhesive layer, an oxygen barrier layer, and a second adhesive layer; and a second laminate adhered to the second adhesive layer of the first laminate, the second laminate having at least two layers containing a styrene-based polymer and a plurality of rubber particles, the tensile elastic modulus of the first laminate being 450 MPa or less.

Description

Technical Field

[0001] This disclosure relates to multilayer sheets and containers. Background Technology

[0002] Packaging containers for packaged foods, for example, are manufactured by forming multi-layered sheets with oxygen-barrier layers to inhibit food deterioration caused by oxygen (see Patent Document 1). In recent years, a packaging container (also called a dispensing package) has been provided that contains food such as seasonings within its main body, with a notch (hereinafter referred to as a "notch") formed in the lid covering the main body (see Patent Document 2). If the packaging container is pinched and bent with fingers, the lid breaks off from the notch, allowing the food to be removed from the break. The multi-layered sheet disclosed in Patent Document 1 can be used in the lid of such a packaging container (dispensing package).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2022 / 054567

[0006] Patent Document 2: Japanese Patent Application Publication No. 2004-83120 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Based on the inventors' research, there is still room for improvement in the ease of fracture of the multilayer sheet disclosed in Patent Document 1. Therefore, an object of one embodiment of the present invention is to provide a multilayer sheet that can be easily fractured.

[0009] Technical means to solve the problem

[0010] The present invention includes the following embodiments.

[0011] [1] A multilayer sheet comprising: a first laminate having a surface layer, a first adhesive layer, an oxygen barrier layer and a second adhesive layer in sequence; and a second laminate bonded to the second adhesive layer of the first laminate, the second laminate having at least two layers containing a styrene-based polymer and a plurality of rubber particles, the tensile modulus of the first laminate being 450 MPa or less.

[0012] [2] As described in [1], the multilayer sheet has an average particle size of less than 2 μm for multiple rubber particles.

[0013] [3] As described in [1] or [2], the multilayer sheet wherein the standard deviation of the average particle size of the multiple rubber particles is less than 1 μm.

[0014] [4] The multilayer sheet described in any of [1] to [3], wherein the thickness of the surface layer is 10 μm or more and 50 μm or less, and the thickness of the oxygen barrier layer is 5 μm or more and 15 μm or less.

[0015] [5] The multilayer sheet described in any of [1] to [4], wherein the thickness of the first adhesive layer and the second adhesive layer is 10 μm or more and 20 μm or less, respectively.

[0016] [6] A container comprising: a container body having an opening and a lid that closes the opening of the container, the lid being formed of a multilayer sheet as described in any one of [1] to [5].

[0017] The inventors have explored ways to improve the fracture ease of multilayer sheets by increasing the fracture ease of the first laminate in the first and second laminates described above [1]. Given that the second laminate has the same structure, if the first laminate can fracture easily, the multilayer sheet as a whole can fracture easily; therefore, it is important to improve the fracture ease of the first laminate. In one embodiment of the present invention, the fracture ease of the first laminate is improved by carefully designing its structure, while maintaining the same structure of the second laminate. The results of the exploration revealed that when the tensile modulus of elasticity of the first laminate is 450 MPa or less, it fractures more easily than when the tensile modulus exceeds 450 MPa. This means that when the tensile modulus of elasticity of the first laminate is 450 MPa or less, the multilayer sheet as a whole fractures more easily than when the tensile modulus exceeds 450 MPa. That is, a key feature of one embodiment of the present invention is that by using a first laminate with a tensile modulus of elasticity of 450 MPa or less, the fracture ease of the first laminate is improved, thereby improving the fracture ease of the multilayer sheet as a whole.

[0018] The effects of the invention

[0019] According to one embodiment of the present invention, it is possible to provide a multilayer sheet that can be easily broken. Attached Figure Description

[0020] [ Figure 1 This is a schematic cross-sectional view showing one embodiment of a multilayer sheet.

[0021] [ Figure 2 [This is a perspective view showing one implementation of the container.]

[0022] [ Figure 3 ]for Figure 2 The diagram shows a schematic cross-sectional view of the container lid.

[0023] [ Figure 4 To display Figure 2The diagram shows an example of container usage. Detailed Implementation

[0024] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described below.

[0025] Figure 1 This is a schematic cross-sectional view illustrating one embodiment of a multilayer sheet. One embodiment of the multilayer sheet 1, such as... Figure 1 The structure shown is formed by stacking a first laminate 2 and a second laminate 3. The first laminate 2 has a surface layer 21 exposed on one side (surface) of the multilayer sheet 1, a first adhesive layer 22 disposed on the surface opposite to one side (surface) of the surface layer 21, an oxygen barrier layer 23 bonded to the surface layer 21 through the first adhesive layer 22, and a second adhesive layer 24 disposed on the surface of the oxygen barrier layer 23 opposite to the surface layer 21. The second laminate 3 has a substrate layer 31 bonded to the oxygen barrier layer through the second adhesive layer 24, and a back layer 32 disposed on the surface of the substrate layer 31 opposite to the second adhesive layer 24 exposed on the other side (back side) of the multilayer sheet 1.

[0026] The overall thickness of the multilayer sheet 1, considering the viewpoint of ensuring the strength of the molded article obtained from the multilayer sheet 1, may be 200 μm or more, 250 μm or more, or 300 μm or more. The overall thickness of the multilayer sheet 1, considering the viewpoint of suppressing the manufacturing cost of the multilayer sheet 1 and the manufacturing cost of the molded article obtained from the multilayer sheet 1, may be 600 μm or less, 500 μm or less, or 400 μm or less.

[0027] The thickness of the surface layer 21 can be 10 μm or more, 13 μm or more, or 15 μm or more, or it can be 50 μm or less, 48 ​​μm or less, or 46 μm or less. The thickness of the surface layer 21 relative to the overall thickness of the multilayer sheet 1 can be 4% or more. When the surface layer 21 has water vapor barrier properties, considering further improvement of these properties, it is preferably 5% or more, and even more preferably 6% or more. Considering the need to minimize the generation of burrs on the end faces during punching of the multilayer sheet and suppress appearance defects, the thickness of the surface layer 21 relative to the overall thickness of the multilayer sheet 1 can be 20% or less, 18% or less, or 16% or less.

[0028] The thicknesses of the first adhesive layer 22 and the second adhesive layer 24, from the viewpoint of obtaining excellent interlayer adhesive strength, may be 10 μm or more, 12 μm or more, or 14 μm or more, respectively. The thicknesses of the first adhesive layer 22 and the second adhesive layer 24, from the viewpoint of suppressing appearance defects, may be 20 μm or less, 18 μm or less, or 16 μm or less, respectively. The thicknesses of the first adhesive layer 22 and the second adhesive layer 24 may be the same or different. The thicknesses of the first adhesive layer 22 and the second adhesive layer 24, relative to the overall thickness of the multilayer sheet 1, may be 2% or more, 3% or more, or 4% or more, or 10% or less, 8% or less, or 6% or less, respectively.

[0029] The thickness of the oxygen barrier layer 23, from the perspective of improving oxygen barrier properties, can be 5 μm or more, 6 μm or more, or 7 μm or more. The thickness of the oxygen barrier layer 23, from the perspective of obtaining a smoother and better-looking molded article from the multilayer sheet, can be 15 μm or less, 13 μm or less, or 11 μm or less. The thickness of the oxygen barrier layer 23, relative to the overall thickness of the multilayer sheet 1, can be 1% or more, 2% or more, or 8% or less, 6% or less, or 4% or less.

[0030] The thickness of the substrate layer 31, considering the viewpoint of improving the rigidity of the multilayer sheet, can be 100μm or more, 150μm or more, 170μm or more, or 190μm or more. The thickness of the substrate layer 31, considering the viewpoint of improving the thermal conductivity of the multilayer sheet during thermoforming, resulting in a molded product with a better appearance, can be 300μm or less, 270μm or less, or 250μm or less. The thickness of the substrate layer 31, relative to the overall thickness of the multilayer sheet 1, can be 50% or more, 53% or more, 55% or more, or 57% or more, or 80% or less, 75% or less, 70% or less, or 65% or less.

[0031] The thickness of the back layer 32, considering the viewpoint of improving the appearance, can be 20μm or more, 30μm or more, or 40μm or more. The thickness of the back layer 32, considering the viewpoint of reducing the amount of pigment used and suppressing costs when pigment is contained in the back layer 32 by means of laser printing, can be 90μm or less, 80μm or less, or 70μm or less. The thickness of the back layer 32, relative to the overall thickness of the multilayer sheet 1, can be 10% or more, 12% or more, or 14% or more, or 30% or less, 25% or less, or 20% or less.

[0032] The thickness of the first laminate 2 can be 20μm or more, 30μm or more, 40μm or more, or 50μm or more, or it can be less than 120μm, 110μm or less, 100μm or less, or 90μm or less. The thickness of the first laminate 2 relative to the overall thickness of the multilayer sheet 1 can be 10% or more, 12% or more, or 15% or more, or it can be less than 30%, 28% or less, or 26% or less.

[0033] The thickness of the second laminate 3 can be 200μm or more, 220μm or more, or 240μm or more, or it can be less than 300μm, less than 290μm, or less than 280μm. The thickness of the second laminate 3 relative to the overall thickness of the multilayer sheet 1 can be 50% or more, 60% or more, or 70% or more, or it can be less than 90%, less than 88%, or less than 86%.

[0034] To impart water vapor barrier properties to the multilayer sheet 1, the surface layer 21 is preferably composed of an olefin-based polymer. An olefin-based polymer contains one or more olefins as monomer units. Examples of olefin-based polymers include: low-density polyethylene (density: 0.91 g / cm³). 3 Above and below 0.93 g / cm 3 Medium-density polyethylene (density: 0.93 g / cm³) 3 Above and below 0.94 g / cm³ 3 High-density polyethylene (density: 0.94 g / cm³) 3 Above and 0.97 g / cm 3 The following are examples of olefin polymers: linear polyethylene, ethylene-α-olefin copolymers, ethylene-vinyl acetate copolymers, ethylene-based ionomer resins, ethylene-acrylic acid copolymers, ethylene-ethyl acrylate copolymers, ethylene-methacrylic acid copolymers, ethylene-methyl methacrylate copolymers, ethylene-propylene copolymers, homopolymers, block copolymers, and atactic polypropylene. These olefin polymers may be used individually or in combination of two or more. Surface layer 21 is preferably composed of low-density polyethylene and high-density polyethylene.

[0035] The content of olefin polymers in surface layer 21, relative to 100 parts by mass of the total mass of surface layer 21, may be 80 parts by mass or more, 90 parts by mass or more, 95 parts by mass or more, or 100 parts by mass.

[0036] When the surface layer 21 contains low-density polyethylene and high-density polyethylene, the percentage of high-density polyethylene relative to the total mass of low-density polyethylene and high-density polyethylene can be 30% or more by mass, 35% or more by mass, or 40% or more by mass, or 70% or less by mass, 65% or less by mass, or 60% or less by mass. Furthermore, in this case, the density of the mixture of low-density polyethylene and high-density polyethylene can be 0.915 g / cm³. 3 Above, 0.92g / cm 3 Above, or 0.93g / cm 3 The above can also be 0.965 g / cm³. 3 Below, 0.96g / cm 3 Below, or 0.95g / cm 3 the following.

[0037] The surface layer 21 may further contain polymers other than olefin polymers, and may also contain additives. Examples of additives include: colorants such as pigments and dyes, release agents such as silicone oils and alkyl esters, fibrous reinforcing agents such as glass fibers, granular lubricants such as talc, clay, and silica, salt compounds of sulfonic acids and alkali metals, antistatic agents such as polyalkylene glycols, ultraviolet absorbers, and antibacterial agents.

[0038] Considering the viewpoint of appropriately bonding different types of layers together, the first adhesive layer 22 and the second adhesive layer 24 are preferably containing a modified olefin polymer. A modified olefin polymer is a polymer obtained by modifying an olefin polymer containing one or more olefins as monomer units. Examples of modified olefin polymers include: polymers obtained by modifying homopolymers of olefins (e.g., olefins with 2 to 8 carbon atoms); polymers obtained by modifying copolymers of olefins (e.g., olefins with 2 to 20 carbon atoms); and polymers obtained by modifying copolymers of olefins (e.g., olefins with 2 to 20 carbon atoms) and vinyl compounds.

[0039] Examples of olefins mentioned above include: ethylene, propylene, butene-1, 3-methylbutene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1, and decene-1. Examples of vinyl compounds mentioned above include: vinyl acetate, vinyl chloride, acrylic acid, methacrylic acid, acrylates, and methacrylates. Copolymers of olefins may also be olefin-based rubbers such as ethylene-butene-1 copolymers and propylene-butene-1 copolymers.

[0040] Regarding modification methods, one example is acid modification under grafting reaction conditions. The acid used in acid modification can be unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, iconic acid, citralic acid, tetrahydrophthalic acid, or their derivatives such as acyl halides, amides, imides, anhydrides, and esters. These derivatives can also be maleic chloride, maleimide, maleic anhydride, citralic anhydride, monomethyl maleate, dimethyl maleate, glycidyl maleate, etc.

[0041] The modified olefin polymer is preferably an unsaturated dicarboxylic acid or its anhydride, more preferably one or more selected from modified ethylene polymers, modified propylene polymers, modified ethylene-propylene copolymer rubbers, and modified ethylene-butene-1 copolymer rubbers modified with maleic acid or its anhydride.

[0042] The modified olefin polymer can be used alone or in combination of two or more. The modified olefin polymer used in the first adhesive layer 22 and the modified olefin polymer used in the second adhesive layer 24 can be the same or different.

[0043] The content of the modified olefin polymer in the first adhesive layer 22, relative to 100 parts by mass of the total mass of the first adhesive layer 22, may be 80 parts by mass or more, 90 parts by mass or more, 95 parts by mass or more, or 100 parts by mass. The content of the modified olefin polymer in the second adhesive layer 24, relative to 100 parts by mass of the total mass of the second adhesive layer 24, may also be 80 parts by mass or more, 90 parts by mass or more, 95 parts by mass or more, or 100 parts by mass.

[0044] The first adhesive layer 22 and the second adhesive layer 24 may further contain additives. Examples of additives are the same as those for additives that may be contained in the surface layer 21.

[0045] Oxygen barrier layer 23 has oxygen barrier properties. Specifically, oxygen barrier layer 23 may also have a density of 5 cc / m 2 Oxygen permeability below 1.5 atm. In this specification, oxygen permeability refers to the oxygen permeability measured according to JIS K7126-2.

[0046] The oxygen barrier layer 23 contains a polymer capable of imparting oxygen barrier properties (oxygen barrier polymer). Examples of oxygen barrier polymers include ethylene-vinyl alcohol copolymer, polyamide, polyvinyl alcohol, and polyvinylidene chloride. One type of oxygen barrier polymer may be used alone, or two or more may be used in combination. From the viewpoint of facilitating the extrusion of the oxygen barrier layer 23, it is preferable that the oxygen barrier layer 23 contains an ethylene-vinyl alcohol copolymer.

[0047] Ethylene-vinyl alcohol copolymers, for example, can be obtained by saponifying ethylene-vinyl acetate copolymers. Considering the need to further enhance the oxygen barrier properties of the oxygen barrier layer 23 and facilitate its extrusion, the content of ethylene units in the ethylene-vinyl alcohol copolymer, based on the total mass of monomer units contained in the copolymer, can be 10 mol% or more, 20 mol%, or less than 65 mol% or less, or less than 50 mol%. The degree of saponification of the ethylene-vinyl alcohol copolymer can be 90 mol% or more, or 95 mol% or more.

[0048] The content of the oxygen barrier polymer in the oxygen barrier layer 23, relative to 100 parts by mass of the total mass of the oxygen barrier layer 23, may be 80 parts by mass or more, 90 parts by mass or more, 95 parts by mass or more, or 100 parts by mass.

[0049] The oxygen barrier layer 23 may further contain polymers other than oxygen barrier polymers, and may also contain additives. Examples of additives are the same as those that may be contained in the surface layer 21.

[0050] The substrate layer 31 contains a styrene-based polymer and a plurality of rubber particles dispersed within the styrene-based polymer. Examples of methods for dispersing the plurality of rubber particles within the styrene-based polymer include graft polymerization of a styrene-based monomer in the presence of a diene-based rubber. This method yields a graft polymer having a structure in which a plurality of rubber particles are dispersed within the styrene-based polymer. Examples of styrene-based monomers include styrene, α-methylstyrene, p-methylstyrene, dimethylstyrene, p-tert-butylstyrene, and chlorostyrene. Examples of diene-based rubbers include polybutadiene rubber, polystyrene-butadiene copolymer rubber, polyisoprene rubber, and polychloroprene rubber.

[0051] Examples of styrene-based polymers with multiple dispersed rubber particles include high-impact polystyrene (HIPS) and polystyrene-acrylonitrile graft polymers (ABS). HIPS, for example, can be obtained by polymerizing styrene monomers in the presence of a diene rubber (typically polybutadiene), and has an island structure where the styrene polymer is the continuous phase (sea), and a rubber grafted from a portion of the styrene monomers forms the dispersion layer (island). ABS, on the other hand, can be obtained by polymerizing styrene monomers and acrylonitrile monomers in the presence of a diene rubber (typically polybutadiene), and has an island structure where a styrene-acrylonitrile copolymer (AS) is the continuous phase (sea), and a rubber grafted from a portion of both styrene and acrylonitrile monomers forms the dispersion layer (island).

[0052] The substrate layer 31 may further contain a styrene-based polymer in which rubber particles are not dispersed. Examples of styrene-based polymers in which rubber particles are not dispersed include homopolymers or copolymers of styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, dimethylstyrene, p-tert-butylstyrene, and chlorostyrene, as well as copolymers of styrene monomers with other monomers. Examples of copolymers of styrene monomers with other monomers include styrene-acrylonitrile copolymers. A single styrene polymer may be used, or two or more may be used in combination.

[0053] Considering the ease of thermoforming the molded article from the multi-layer sheet 1 and the excellent rigidity of the molded article, the substrate layer 31 is preferably composed of high-impact polystyrene (HIPS) and styrene homopolymer (general-purpose polystyrene, GPPS). In addition, by mixing GPPS into HIPS, the advantage of easily adjusting the rubber particle content in HIPS can also be obtained.

[0054] In the substrate layer 31, the content of styrene-based polymers dispersed among multiple rubber particles, relative to the total mass of 100 parts by mass of the substrate layer 31, can be 60 parts by mass or more, 65 parts by mass or more, or 70 parts by mass or more, or 95 parts by mass or less, 90 parts by mass or less, or 85 parts by mass or less. In the substrate layer 31, the content of styrene-based polymers not dispersed among rubber particles, relative to the total mass of 100 parts by mass of the substrate layer 31, can be 5 parts by mass or more, 10 parts by mass or more, or 15 parts by mass or more, or 40 parts by mass or less, 35 parts by mass or less, or 30 parts by mass or less.

[0055] The content of styrene-based polymers in the substrate layer 31 (the total content of styrene-based polymers dispersed in rubber particles and styrene-based polymers not dispersed in rubber particles) may be 90 parts by mass or more, 95 parts by mass or more, or 98 parts by mass or more, relative to 100 parts by mass of the total mass of the substrate layer 31.

[0056] The average particle size (also called "rubber average particle size") of the multiple rubber particles dispersed in the styrene-based polymer can be less than 2 μm, less than 1.8 μm, less than 1.6 μm, less than 1.4 μm, or less than 1.2 μm. When the rubber average particle size is less than 2 μm and a notch is formed on the second laminate 3 for use as a cover (details to follow), cracking becomes easier when the cover is bent, starting from the notch and propagating in the second laminate 3. As a result, the multilayer sheet can easily break without depending on the breaking speed. The rubber average particle size can also be greater than 0.1 μm, greater than 0.5 μm, or greater than 0.8 μm. The rubber average particle size in this specification refers to the arithmetic mean particle size based on the particle size distribution on a volume basis as measured by a laser diffraction / scattering particle size analyzer.

[0057] The standard deviation of the average rubber particle size, considering the view that the multilayer sheet 1 can easily break further without depending on the breaking speed when it breaks, can also be less than 1.0 μm, less than 0.8 μm, less than 0.6 μm, or less than 0.4 μm. The standard deviation of the average rubber particle size can also be greater than 0.05 μm, greater than 0.1 μm, or greater than 0.15 μm.

[0058] The content of rubber particles in the substrate layer 31, considering the viewpoint of improving crack transmission, can be less than 7% by mass or less than 6% by mass, based on the total mass of the substrate layer 31. The content of rubber particles in the substrate layer 31, considering the viewpoint of improving the impact resistance of the multilayer sheet 1, can be more than 3% by mass or more than 4% by mass, based on the total mass of the substrate layer 31.

[0059] When printing is performed on multilayer sheet 1 using laser irradiation or other methods on its formed products, the substrate layer 31 may further contain a white pigment (or a masterbatch containing the white pigment). Examples of white pigments include: titanium dioxide (titanium white), zinc oxide (zinc white), zinc barium white, lead white, etc.

[0060] The content of white pigment, considering the need for good opacity to improve the color rendering of printed text and light-blocking properties to suppress light-induced discoloration and alteration of the contents, can be 1 phr or more, 2 phr or more, or 3 phr or more. The content of white pigment, considering the need to suppress white pigment aggregation to prevent appearance defects caused by agglomerates in multilayer sheets 1 and their molded products, can be 7 phr or less, or 6 phr or less. The unit phr used here refers to the mass fraction of white pigment relative to the total mass of polymer contained in 100 parts by mass of the substrate layer 31.

[0061] The substrate layer 31 may further contain polymers other than those mentioned above, and may also contain additives. Examples of additives include: compatibilizers to make different components compatible, colorants such as pigments and dyes, release agents such as silicone oil and alkyl esters, fibrous reinforcing agents such as glass fibers, granular lubricants such as talc, clay, and silica, salt compounds of sulfonic acids and alkali metals, antistatic agents such as polyalkylene glycols, ultraviolet absorbers, and antibacterial agents. Additionally, the substrate layer 31 may further contain waste resin generated during the manufacturing process of multilayer sheets and containers.

[0062] The back layer 32 contains a styrene-based polymer with multiple rubber particles dispersed. The details of the styrene-based polymer with multiple rubber particles dispersed are the same as those described in the substrate layer 31.

[0063] In the back layer 32, the content of styrene-based polymer dispersed in rubber particles may be 90 parts by mass or more, 95 parts by mass or more, or 98 parts by mass or more, relative to 100 parts by mass of the total mass of the back layer 32.

[0064] The content of rubber particles in the back layer 32, based on the total mass of the substrate layer 31, can be less than 8% by mass or less than 7% by mass, taking into account the viewpoint of improving crack transmission. The content of rubber particles in the substrate layer 31, taking into account the viewpoint of improving the impact resistance of the multilayer sheet 1, can be more than 4% by mass or more than 5% by mass.

[0065] When printing is performed on the multilayer sheet 1 using laser irradiation, the back layer 32 may further contain a pigment (or a masterbatch containing such pigment) that develops color upon laser (e.g., YAG laser) irradiation. Examples of such pigments include: mica, titanium dioxide, antimony oxide, copper phosphates, sulfate-like metal salts, and carbon black. The content of this pigment may be 0.007% by mass or more, or 0.009% by mass, or 4.6% by mass or less, or 3.2% by mass or less.

[0066] The back layer 32 may further contain other polymers besides the polymers mentioned above, and may also contain additives. Examples of additives are the same as those that may be contained in the substrate layer 31.

[0067] In the multilayer sheet 1 described above, the tensile modulus of the first laminate 2 is 450 MPa or less. Therefore, the first laminate 2 can easily fracture, resulting in the multilayer sheet 1 also easily fractureing. The tensile modulus of the first laminate 2 can be 440 MPa or less, 430 MPa or less, 420 MPa or less, 330 MPa or less, or 200 MPa or less, or it can be 100 MPa or more, 150 MPa or more, 200 MPa or more, 250 MPa or more, 300 MPa or more, or 340 MPa or more. Here, the tensile modulus of elasticity refers to the larger of the tensile modulus of elasticity in the flow direction (MD) and the tensile modulus of elasticity in the width direction (TD), which is perpendicular to the MD direction, of the multilayer sheet 1.

[0068] The layer composition of the multilayer sheet is not limited to that described in the above embodiments. Figure 1The layer structure is shown in the diagram. For example, in the above embodiment, the second laminate 3 has a substrate layer 31 and a back layer 32, which are two layers containing a styrene-based polymer and multiple rubber particles. However, at least two layers containing a styrene-based polymer and multiple rubber particles are sufficient, and in other embodiments, there may be three or more layers. In addition, for example, in the above embodiment, the back layer 32 is exposed, but in other embodiments, a design layer (printed layer) with text and patterns may be further provided on the side of the back layer opposite to the substrate layer. This design layer may be a PET film or may be provided through a lamination process.

[0069] The manufacturing method for multilayer sheets is not particularly limited, and general methods can be used. For example, multilayer sheets can be manufactured using multiple extrusion machines by melt co-extrusion, where the raw materials for each layer are stacked in a molten state. More specifically, examples include: using multiple single-shaft or bi-shaft extruders to melt and extrude the raw materials for each layer, obtaining multilayer sheets through a feed block with selective plugs and a T-die; and using a multi-manifold die to obtain multilayer sheets.

[0070] Multilayer sheets can be thermoformed, therefore, molded articles can be obtained by forming the aforementioned multilayer sheets. There are no particular limitations on the types of molded articles; examples include, for instance, container lids, and in particular, lids of food packaging containers as suitable embodiments.

[0071] Figure 2 This is a perspective view showing one implementation of the container. (e.g.) Figure 2 As shown, one embodiment of the container 10 includes a container body 11 having a space for holding contents and a lid 12. In this embodiment, the container body 11 has two spaces for holding two kinds of contents, and an opening 11a is provided on the upper surface corresponding to the space. The lid 12 is fixed to the upper surface of the container body 11 to cover the opening 11a. The lid 12 has a notch (cut) 13 provided so that the lid 12 can be broken by bending it. A connecting portion 14 is provided between the space for holding contents and the notch 13. Each connecting portion 14 has an easy-peeling portion 15. The easy-peeling portion 15 is a part that is fixed to the container body 11 in a way that makes the lid 12 easier to peel off than other parts. Before use, the container 10 is fixed to the container body 11 by the lid 12 at the easy-peeling portion 15, and the two spaces for holding contents are independent of each other. Such a container 10 is also called a dispensing package. In addition, as another implementation, when a content is contained in two spaces, the easy-to-peel part 15 may not be provided, and the two spaces may be connected.

[0072] Figure 3 This is a schematic cross-sectional view of the cover 12. Figure 3 As shown, the cover 12 is formed of the aforementioned multilayer sheet 1 and has the same layer structure as the multilayer sheet 1. A notch (cutout) 13 is provided in the cover 12, extending from the back layer 32 to the substrate layer 31. The cover 12 is disposed on the container body 11 such that the surface layer 21 faces the container body 11 (contents), and the back layer 32 is exposed.

[0073] Figure 4 This is a schematic diagram illustrating an example of using container 10. Container 10 independently holds a first content C1 and a second content C2. The user U can crack the container 10 by pinching it with their fingers and bending it (bending it so that the lid 12 is facing outwards). Figure 2 and Figure 3 The notch 13 shown in the image serves as the starting point, and the contents extend in the stacking direction of the cover 12. Simultaneously, the first contents C1 and the second contents C2 exert pressure on the cover 12 from the surface layer 21 side. Due to this cracking and pressure, the cover 12 breaks near the notch 13 and is peeled off from the container body 11 at the easily peelable portion 15. Thus, the space containing the first contents C1 and the second contents C2 connects with the break in the cover 12 at the connecting portion 14. As a result, the first contents C1 and the second contents C2 are discharged from the break in the cover 12 through the connecting portion 14 to the outside of the container 10. At this time, because the cover 12 is formed of a multilayer sheet 1 having the aforementioned easily breakable first stack 2, the cover 12 easily breaks due to the pressure of the first contents C1 and the second contents C2.

[0074] [Example]

[0075] The present invention will be described in more detail below with examples and comparative examples, but the present invention is not limited to the content of the examples, etc.

[0076] <1. Fabrication of Multi-Layer Sheets>

[0077] The raw materials used in the examples and comparative examples are as follows.

[0078] (1) Surface layer

[0079] Low-density polyethylene (LDPE): "LC522" (Japan Polyethylene Co., Ltd.)

[0080] High-density polyethylene (HDPE): "HF562" (Japan Polyethylene Co., Ltd.)

[0081] (2) First adhesive layer and second adhesive layer

[0082] Modified polyolefin (modified PO): "Modic F502C" (Mitsubishi Chemical Corporation)

[0083] (3) Oxygen barrier layer

[0084] Ethylene-vinyl alcohol copolymer (EVOH): “EVAL J171B” (Kuraray Corporation)

[0085] (4) Second layer stack

[0086] High Impact Polystyrene (HIPS) 1: "H485" (Toyo Styrene Co., Ltd., average rubber particle size: 1μm)

[0087] High Impact Polystyrene (HIPS) 2: "E640N" (Toyo Styrene Co., Ltd., average rubber particle size: 3μm)

[0088] High Impact Polystyrene (HIPS) 3: "H850N" (Toyo Styrene Co., Ltd., average rubber particle size: 4μm)

[0089] • Homopolymer of Styrene (GPPS): “HRM23” (Toyo Styrene Co., Ltd.)

[0090] White pigment masterbatch: "ET3627" (Rihong BICS Co., Ltd., white pigment (titanium oxide) concentration in the masterbatch: 50% by mass).

[0091] Printing masterbatch: "TT3344" (Resino Color Industry Co., Ltd.)

[0092] (Example 1)

[0093] The mixture is prepared by mixing HDPE and LDPE in a 50 / 50 mass ratio (density of polyethylene: 0.941 g / cm³). 3 The mixtures were prepared by mixing modified PO, EVOH, HIPS1 and GPPS at a mass ratio of 80 / 20, and further mixing 5 pr of white pigment masterbatch, and by mixing 7 pr of printing masterbatch in HIPS. The mixtures were melt-extruded from Φ75mm single-shaft extruder, Φ45mm single-shaft extruder, Φ120mm single-shaft extruder and Φ65mm single-shaft extruder, respectively, and obtained by feeding block method. The resulting multilayer sheet has a thickness of 330μm and a width of 640mm, consisting of a surface layer of 30μm, an adhesive layer of 15μm, an oxygen barrier layer of 10μm, an adhesive layer of 15μm, a substrate layer of 210μm and a back layer of 50μm.

[0094] (Example 2 and Comparative Examples 1 and 2)

[0095] The thickness of each layer was changed as shown in Table 1. Otherwise, the process was the same as in Example 1 to obtain a multilayer sheet.

[0096] (Example 3)

[0097] The mixing ratio of HDPE and LDPE in the surface layer was changed to HDPE / LDPE = 30 / 70 (mass ratio), and the density of polyethylene was set to 0.934 g / cm³. 3 The thickness of each layer was changed as shown in Table 1. Otherwise, the process was the same as in Example 1 to obtain a multilayer sheet.

[0098] (Comparative Example 3)

[0099] Using HIPS2 instead of HIPS1, the process was otherwise the same as in Comparative Example 1 to obtain a multilayer sheet.

[0100] (Comparative Example 4)

[0101] Using HIPS3 instead of HIPS1, the process was otherwise the same as in Comparative Example 1 to obtain a multilayer sheet.

[0102] <2. Characteristic Evaluation>

[0103] The multilayer sheets of the obtained embodiments and comparative examples were evaluated using the following methods.

[0104] (A) Thickness of each layer

[0105] Test pieces were cut at five equally spaced locations along the width direction (TD) perpendicular to the flow direction (MD) of the multilayer sheet, using a single-edged blade to create cross-sections. The cross-sections of the test pieces were observed using a real-world microscope (VK-X100 shape measurement laser microscope, manufactured by Keynes). The thickness of each layer was measured. The thickness of each layer was calculated as the average thickness of the layers at the five width-direction locations of the multilayer sheet.

[0106] (B) Average particle size of rubber in the substrate layer and backing layer

[0107] Test pieces were cut from a multilayer sheet at arbitrary locations, and layers other than the substrate layer and backing layer were removed using a single-edged blade, thus exposing the substrate layer and backing layer. Next, the components other than the rubber particles were dissolved in a solvent (N,N-dimethylformamide) to separate the rubber particles, and then the average particle size of the rubber particles in the substrate layer and backing layer was measured using a laser diffraction / scattering particle size analyzer (Horiba Manufacturing Co., Ltd., model: LA-920).

[0108] (C) Tensile modulus of elasticity of the first layer

[0109] Cut a 10mm × 150mm strip (Type 2) of test piece, as described in JIS K7127:1999, at any point on the first laminate. Using a tensile testing machine (Toyo Seiki Co., Ltd., model VE1D) according to JIS K7161:2014, stretch the test piece along its long side. Under a testing environment of 23°C and 50%RH, measure the tensile modulus (MPa) at a clamping distance of 50mm and a tensile speed of 200mm / min. The tensile modulus is measured in both the MD and TD directions of the first laminate (test piece).

[0110] (D) Fracture ease (fracture strength) of the first layer of the composite

[0111] Using the same method as for tensile modulus of elasticity, the test piece is stretched along its long side, and the strength at which the test piece breaks is evaluated as the breaking strength (MPa). The lower the breaking strength of the first layer, the easier the first layer is to break.

[0112] The multilayer sheets obtained in the embodiments and comparative examples were evaluated using the evaluation method for multilayer sheets described above. The results are shown in Table 1.

[0113] [Table 1]

[0114]

[0115] In addition, the fracture susceptibility of each second laminate used in the examples and comparative examples was evaluated. Specifically, a test piece measuring 15mm × 150mm was cut from the second laminate at any position, and the two ends of the long side of the test piece were clamped in an MIT flexural endurance tester (MIT-D, manufactured by Toyo Seiki Co., Ltd.). Under a load (250g) applied to the test piece, it was bent at a bending angle of 135° and at two bending speeds (high speed: 175rpm, low speed: 90rpm). The number of bends required for the test piece (second laminate) to break into two pieces was measured. The evaluation was based on the number of bends according to the following criteria. The fewer the number of bends, the easier it is for the second laminate to break.

[0116] A: Number of bends less than 50

[0117] B: The number of bends is more than 50 but less than 100.

[0118] C: The number of bends is more than 100 but less than 1000.

[0119] D: Bending more than 1000 times

[0120] The results are as follows: The second-layer stacks in Examples 1-3 and Comparative Examples 1-2 were rated "A" at both high and low speeds. The second-layer stack in Comparative Example 3 was rated "B" at high speed and "C" at low speed. The second-layer stack in Comparative Example 4 was rated "C" at both high and low speeds.

[0121] [Symbol Explanation]

[0122] 1: Multi-layer sheet

[0123] 2: First layer of stacked body

[0124] 21: Surface layer

[0125] 22: First adhesive layer

[0126] 23: Oxygen Barrier Layer

[0127] 24: Second adhesive layer

[0128] 3: Second layer of stacked body

[0129] 31: Substrate layer

[0130] 32: Back layer

[0131] 10: Container

[0132] 11:Container body

[0133] 12: Cover

[0134] 13: Notch

[0135] 14: Connecting parts

[0136] 15: Easily peelable section

[0137] U: User

[0138] C1: First Content

[0139] C2: Second contents.

Claims

1. A multilayer sheet material, comprising: A first laminate comprising a surface layer, a first adhesive layer, an oxygen barrier layer, and a second adhesive layer in sequence; and The second laminate bonded to the second adhesive layer of the first laminate, The second laminate has at least two layers containing styrene-based polymers and multiple rubber particles. The tensile modulus of elasticity of the first laminate is below 450 MPa.

2. The multilayer sheet as described in claim 1, wherein, The average particle size of the plurality of rubber particles is less than 2 μm.

3. The multilayer sheet as described in claim 1 or 2, wherein, The standard deviation of the average particle size of the plurality of rubber particles is less than 1 μm.

4. The multilayer sheet as described in claim 1 or 2, wherein, The thickness of the surface layer is 10 μm or more and 50 μm or less, and the thickness of the oxygen barrier layer is 5 μm or more and 15 μm or less.

5. The multilayer sheet as described in claim 1 or 2, wherein, The thicknesses of the first adhesive layer and the second adhesive layer are respectively greater than 10 μm and less than 20 μm.

6. A container comprising: a container body having an opening, and a lid that closes the opening of the container. The cover is formed of a multilayer sheet as described in claim 1 or 2.

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